1. Field of the Invention
The present invention relates to a method and apparatus for image forming, and more particularly to a method and apparatus for image forming that can perform an effective mixing of development agent.
2. Discussion of the Background
In a recent background image forming apparatus shown in FIG. 1, a development mechanism using a two-component development agent typically includes a development roller 5, and transfer screws 6 and 7 for transferring the development agent inside a housing (not shown) of the development mechanism arranged adjacent to an image carrying member 12. In this type of the two-component development mechanism, the transfer screws 6 and 7 are arranged in parallel to each other and one of the two is placed close to and in parallel to the development roller 5 in the width direction thereof. The other of the two is placed farther from, and in parallel to, the development roller 5 in the width direction thereof. The development agent is circulated using the thus-configured two transfer screws 6 and 7.
The transfer screws 6 and 7 perform mixture and transfer of the development agent in a superior manner in a direction X in parallel to a length direction of the development roller 5. However, the transfer of the development agent in a direction Y orthogonal to the length direction of the development roller 5 is not performed in a manner as good as that performed in the direction X.
Accordingly, the transfer screw 6 arranged closer to the development roller 5 is prone to cause an uneven density in a form of a screw pitch when a great amount of toner is being supplied. Particularly, in a color copying machine, the uneven density appears as an unevenness of color and therefore it greatly reduces image quality.
The present invention provides a novel image forming apparatus. In one example, a novel image forming apparatus includes a development mechanism using a two component development agent and which includes a development roller and first and second transfer screws. The first transfer screw includes a first number of screw spirals for transferring the development agent from a first end of the first transfer screw to a second end of the first transfer screw and conveying the development agent to the development roller. The first transfer screw is arranged approximately horizontal and in parallel to the development roller. The second transfer screw includes a second number of screw spirals for transferring the development agent from a first end of the second transfer screw to a second end of the second transfer screw and conveying the development agent from the second end of the second transfer screw to the first end of the first transfer screw. The second transfer screw is arranged approximately horizontal and in parallel to the first transfer screw. In this development mechanism, the first and second numbers of the screw spirals are different from each other.
The first number of the screw spirals may be greater than the second number of screw spirals.
The first transfer screw may have a first spiral pitch which is greater than a second spiral pitch of the second transfer screw.
In the above-mentioned image forming apparatus, when the first and second transfer screws have spiral diameters equal to each other and shaft diameters equal to each other, the first and second transfer screws may satisfy relationships of:
P1xe2x89xa71.5xc3x97P2; and
S1xe2x89xa74xc3x97S2,
wherein P1 and S1 represent the first spiral pitch and the first screw spirals, respectively, of the first transfer screw and P2 and S2 represent the second spiral pitch and the second screw spirals, respectively, of the second transfer screw.
The first and second transfer screws may be rotated in directions different from each other.
The present invention further provides a novel method of transferring development agent. In one example, a novel method includes the steps of providing, placing, rotating, and reverse rotating. The providing step provides a first transfer screw at a position approximately horizontal and in parallel to a development roller. The first transfer screw has a first number of screw spirals. The placing step places a second transfer screw at a position approximately horizontal and in parallel to the first transfer screw. The second transfer screw has a second number of screw spirals in parallel to the first transfer screw. In this case, the second number of screw spirals is different from the first number of screw spirals. The rotating step rotates the first transfer screw. The reverse rotating step rotates the second transfer screw in a reverse direction relative to the rotation of the first transfer screw to transfer the development agent in a direction from a first end of the second transfer screw to a second end of the second transfer screw and in a direction from the second transfer screw to the first transfer screw so that the development agent is consequently transferred by the first transfer screw in a direction from a first end of the first transfer screw to a second end of the first transfer screw and in a direction from the first transfer screw to the development roller.
The first number of the screw spirals may be greater than the second number of the screw spirals.
The first transfer screw may be a first spiral pitch which is greater than a second spiral pitch of the second transfer screw.
In the above-mentioned method, when the first and second transfer screws have spiral diameters equal to each other and shaft diameters equal to each other, the first and second transfer screws satisfy relationships of:
P1xe2x89xa71.5xc3x97P2; and
S1xe2x89xa74xc3x97S2,
wherein P1 and S1 represent the first spiral pitch and the first screw spirals, respectively, of the first transfer screw and P2 and S2 represent the second spiral pitch and the second screw spirals, respectively, of the second transfer screw.
The first and second transfer screws may be rotated in directions different from each other.